I've always thought that any car or truck after 1973 was unleaded. I remember my 1974 chevy had unleaded on the gas gauge. I alway expected that trucks were that way also. Last night I read a book that stated that trucks did not become unleaded until mid 1975. Anyone have any input on this.....

Thanks,
Fred.

Depends on what you mean by "unleaded".

It's illegal to use leaded gas in a vehicle with a cat converter. Cats started in '75, but they were not universal. I had a '80 Honda that did not have a cat, but that was probably the last non-catalyst-equipped car sold in America.

Anything GM built after '71 has hardened exhaust valve seats, so using unleaded shouldn't be a problem until you valve job deeper than the induction hardening. Once you're into softer iron,the seats can go away in a hurry, depending on the load the engine sees.

Trucks were later for everything, including safety devices.

Schurkey,

Yeah, that's what I was looking for, so 72 and after where harded seats. One more question if you don't mind. If you do a valve job, will grinding the seats put you into the soft metal? Or could you do one valve job and still be ok?

Tnanks,
Fred.

i seem to remember something about 3/4 ton and bigger trucks being considered "commercial" vehicles and were exempted from several upgrades for at least a couple of years. now that may have been just a michigan thing. the first cars to get cat converters was definetly '75. they had to change the ramps (add a riser) on the rail cars that shipped them for clearance because the first ones hung down quite a bit below the undecarriage of a typical sedan.

Fred,
Depends on how bad the seats are worn. The factory seats were induction hardened and it was not real "deep". If the exhaust seats are really beat out, chances are that hardened seat inserts should be installed in the heads. If they are in good shape, you might be able to get away without them. Hard to say without looking at the heads.

Originally posted by BillK:
Fred,
Depends on how bad the seats are worn. The factory seats were induction hardened and it was not real "deep". If the exhaust seats are really beat out, chances are that hardened seat inserts should be installed in the heads. If they are in good shape, you might be able to get away without them. Hard to say without looking at the heads. do you know if bbc 990 heads had hardened seats? or maybe some did some didnt? and if so were they induction hardened? also how much risk is there in machining and installing hardened seats. i bought a set of sbc heads a while back that had had hardened seats installed when the heads were rebuilt. they very quickly cracked out in this area and leaked coolant into the chamber. is this a unique thing or in your experience have you seen it to be a common problem? thanks for the info (BTW i love having you and mike on here for some real pro advice and if we dont say often enough that we appreciate let me correct that).